Method of making bifocal lenses.



W. BAUSGH. METHOD OF MAKING BIFOGAL LENSES.

APPLICATION FILED SEPT. 6, 1907.

Patented Aug. 10, 1909.

3 vwz Mic L Witmzoozo UNITED STATES PATENT OFFICE.

WILLIAM BAUSOH, OF ROCHESTER, NEW YORK, ASSIGNOR, BY M'ESNE ASSIGNMENTS, TO BAUSCH & LOMB OPTICAL COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION. OF

NEW YORK, (NO. 2.)

. METHOD OF MAKING BIFOGAL LENSES.

Nessa-s26.

Specification of LettersPatent.

Patented Aug. 10, 1909.

Application filed September 6, 1907. Serial No. 391,574. 1

To all whom it may concern-.-

Be it known that I, WILLIAM BAUSGH, of Rochester, in the county of Monroe and State of New York, have invented certain new and useful Improvements in Methods of Making Bifocal Lenses; and I do hereby declare the following to be a full, clear, and exact description of the same, reference being had to the accompanying drawings, forming a part of the specification, and to the reference-numerals marked thereon.

My present invention relates to the manufacture of lenses embodying two or more parts or members composed of glass of different refractive index and consists in an improved method whereby' only one of the members is required to be ground and polished, and this the male or positive member which is the one that may be subjected'to these operations with the least expense.

Bifocal lenses for spectacles and eyeglasses as usually constructed, embody a major lens formed of glass of one refractive index, relatively low, such as crown glass adapted for .distant vision and a minor lens of flint glass of relatively higher refractive index adapted fo'rnear vision, smaller than the former and secured Within its peripherynear the lower edge bycement or some securing medium, both faces of both the major and minor lens being previously ground and polished and their proximate faces being accurately fitted to each other, usually by rinding and polishing a concavity in the ace of the major lens of exactly the curve of the corresponding face of the minor lens. Naturally, accurate work is required in making such lenses and their cost is relatively high. Furthermore, the balsam or cement used in securin the parts together is liable to become disco ored and to vary in density and refractive power, and to crack or lose its adhesive. power, owing to differences in the coefficient of expansion of glass of different com osition, thereby rendering the lenses wort less for the purposes of vision until properly repaired. All these objections in manufacture and efficiency are overcome by my invention and my lenses may be made cheaply and will always remain the same.

In the manufacture of bifocal spectacle and eyeglass lenses, it is first necessary to determine the kinds of glass to be employed for the major and minor lenses and the to produce the optical effect desired, and in carrying out my invention after this is determined I first grind the inner face or surface of the minor lens to the required curve and polish it, or if desired both surfaces thereof may be ground and polished I then take a piece of glass selected for the major lens and having a lower refractive index, such as crown glass, and heat it until its body becomes more or less plastic and. its surface is practically fused, and after also heating the minor lens slightly to prevent cracking but, so that its surface conformation will not be changed by pressure, I place the minor lens upon the former with its curved face down and force it down into the glass for the major lens embedding its lowc'r surface in the latter and causing the twoto become firmly united and practically integral. This lower ground and polished, face of the minor lens therefore displaces the glass of the major lens and obviates the ne'- cessity heretofore existing of grindinga recess'in the inner face of the major lens next the minor and polishing it. After the minor is thus embedded in the glass for the major lens, the only operation necessar is to grind and polish the outer faces of the atter in the usua manner on the proper curves to produce the optical effect desired. Of course the outer face of the minor lens may be ground and polished if desired on the curve it is to have in the finished article,- and the Whole lens may be roughly molded at the same time that the minor lens is pressed into it, so that only a small amount of'material is required to be removed by grinding. One of the principal features of the invention however is that the manufacturer may make and sell to Opticians the blanks for bifocal lenses having theminor lenses of dif ferent curves or powers and-of different refractive indices embedded therein and the. Optician knowing the curve, index and position of the minor lensmay then grindthe outer faces of these blanks as required to produce the desired optical effect.

The minor lens for bifocal glasses is usually convexon the surface that is next to the major lens and it is therefore much easier to grind and polish than to grind and,polish a depression in the major lens and as'this rounded surface is v ressed down into the face of the glass for t e major lens and forms its own seat and is not heated sufficiently to lose its shape, the surface of the crown glass does not require finishing at all excepting perhaps to remove imperfections or dust from its surface;

I have found in practice that by subjecting the blank for the crown glass for a few minutes to a temperature of 1500 degrees Fahrenheit in a furnace heated by electricity, it is rendered sufficiently soft to enable the lens of flint glass to be pressed into its surface, form its own seat and become fused in position. The flint glass lens is not left in the. furnace a sufficient length of time to become softened and lose its shape, but is merelyjvarniedso that it will not crack nor separate from the other part. After being formed the complete lens is annealed in the usual manner. a

In the drawings: Figure 1 is a sectional View of the press and the blanks for the major lens and the minor lens separated. Fig. 2 is a similar view after the minor lens has been embedded or pressed into the blank .forthe -major lens and Fig. 3 is a similar view of a complete lens. 7

The blank for the major lens is indicated by 1, the minor lens by 2, and the complete bifocal lens, ground and polished, by 12. The 'only'a paratus necessary for carrying outthe met od is a suitable furnace for heating the blanks and a suitable ress for embedding the minor lens in the lank for the major, embodying a bed 3 and a relatively movable platen 4, indicated in Fig. 1.

Itis im racticable to give the temperatures to w ich the parts should be heated owing to the difficulty in determining exact temperatures and to the character of the glass employed, but I have found those given above as suflicient, but it is essential that the formed lens (preferably the minor lens) should not be heated sufficiently to cause it to change its sha e whenthe two are pressed together, thougii it must be sufficiently heated to cause the partsto'properly unite.

By the use of the term adhesive as descriptive of the condition of the glass for the ma or lens blank, it is not intended that this surface is necessarily flowing or tacky to such an extentthat the mlnor lens will at once stick to it when placed thereon and without pressure, as the proper adhesion or .connection of the parts is obtained by ressure,- even when. the crown glass is ard enough .to permit the minorjlens to rock on its rounded face when first applied, and as well when the surface is tacky Of course compound lenses other than spectacle lenses could be formed in-this same way if desired.

piece of glass while it is lastic, causing it to form a correspondingly s aped recess therein and the two to become fused together.

2. The method of forming blanks for bifocal lenses embodying two pieces of glass of different refractive indices, consisting in piece to form a positive lens surface, warming the lens thus formed, heating the other piece of glass sufficiently to render it plastic and its surface adhesive, ressing the round and polished surface of t e lens into t 1e last mentioned piece while it is plastic to form a correspondingly shaped recess therein and cause the two to adhere.

3. The method of forming bifocal lenses embodying a major and. a minor lens composed of glass of different refractive indices, consisting in grinding and polishing the con vex surface of the minor lens, then warming it, heating the glass for the major lens to render it plastic and its surface adhesive, pressing the convex surface of the minor lens into the surface of the lass for the major lens and grinding and p0 ishing the surfaces of the major lens and the outer or ex osed surface of the minor lens to the desire curvatures.

4. The method of forming lenses of two pieces of glass having different refractive indices, consisting in grinding and polishing the surface of one iece to form a convex lens surface, heating tie other piece until it is plastic, then forcing the. ground and olished surface of the former lens into the b0 y of the latter and finally gradually cooling the lens thus formed.

WILLIAM BAUSCH. Witnesses H. O. TrroN, W. G. WooDwoRTH.

75 grinding and polishing one surface of one. 

